Differentiation of mesenchymal tissues during phallic morphogenesis with emphasis on the os penis: roles of androgens and other regulatory agents.

This article reviews various aspects of differentiation and growth of phallic mesodermal tissues with special reference to the os penis. In many species of certain mammalian orders the penile interior contains an os penis or baculum with bona fide bone. Mechanisms of phenotypic sex differentiation and the androgenic regulation of morphogenesis of genitourinary tracts of both sexes are first overviewed. Thereafter the various mesodermal tissues in fully developed penes and clitorides are discussed. The developmental fate of mesenchymal cells in the fetal genital tubercles is then considered in detail, including considerations of epithelial-mesenchymal interactions. The review concludes with a discussion of the possible roles of certain polypeptide growth factors acting in concert with androgenic steroids. Special emphasis is placed on the potential role of bone morphogenetic proteins in formation of the os penis in a restricted number of eutherian mammalian taxa.